1. Field of this Invention
This invention relates to lined metallic tanks and methods of making same, more particularly those methods involving welding a multi-piece metallic tank without damaging the nonmetallic lining material, and to indirect fired water heaters, more particularly to such heaters having a lined metallic vessel.
2. Prior Art
The tank manufacturing industry has long been plagued with the problems associated with forming a multi-piece metallic tank structure having a nonmetallic lining on its interior. Since such tanks have achieved widespread usage in virtually every field, including hot water storage tanks, hot water heating tanks, accumulators for hot water heating systems, liquid transportation systems, etc., the problem of economically fabricating such tanks is one of substantial magnitude. Due to the enclosed nature of such vessels, they are more easily fabricated in serveral sections which are subsequently welded together. However, when a nonmetallic lining is associated with the tank, the problem of welding the tank sections together is magnified, since it must be done without destroying the continuity of the interior lining. Any break or discontinuity in the lining will result in the eventual contamination of the tank's contents and corrosion of the metal tank.
Several attempts have been made to overcome this problem. One solution has been to apply the coating to the metal tank after it has been welded together, as exemplified in U.S. Pat. No. 2,758,367. However, this drastically limits the types of coating that may be applied to the interior of a closed vessel. Such a process is also time consuming and expensive, and there is no assurance that the lining completely covers the interior of the vessel as intended.
Where a foamed material is utilized as the insulating lining, it may be foamed in situ. This involves the use of an interior and exterior vessel wherein the foam is placed in the space between the two vessels. The plastic bottle may be considered as an interior vessel but not capable of withstanding any appreciable pressure on its own. (The insulation obtained by foaming in place is different from the design of this invention where the foam is formed into the desired shape from a separate mold.) Processes utilizing these concepts are shown in U.S. Pat. Nos. 3,313,020 and 3,328,496. This process is more expensive since it requires the use of two vessels. The foam must also be foamed in small sections to allow for the complete escape of the gases generated by the foaming process and, therefore, such method is unduly time consuming when fabricating large vessels or tanks.
Another method of fabricating lined, multi-piece metallic vessels involves the use of a chill ring placed in the interior of the metallic vessel adjacent the weld area. The chill ring is usually an annular metal structure, which may or may not have a coating thereon, and serves to absorb the heat generated by the welding process such that it does not destroy the tank lining. But chill rings do not protect the material inside of the tank directly underneath the chill rings. The use of chill rings are well-known and are shown in U.S. Pat. Nos 2,412,271 and 2,970,719. The drawbacks to such system are obvious, insofar as the use of a separate structure increases the cost and weight of the tank while serving effectively no useful purpose once the tank is welded together.
It is also known to utilize a rubber material as an insulating band installed adjacent to a welding area, as set forth in U.S. Pat. No. 2,587,840. However, the purpose of this insulating band is not to protect the lining of the tank since there is no lining in the area which the band is used, but to prevent the current generated by the electric welding process form jumping to an adjacent metallic wall. Other methods of fabricating welded vessels are set forth in U.S. Pat. Nos. 845,760, 2,113,060, 2,820,427 and 3,253,731. See also U.S. Pat. Nos. 2,542,543, 2,317,734, 1,549,721, 4,099,641, 2,729,313, 2,263,021, 2,146,381, 2,551,484, 3,358,118, 3,614,967 and 3,326,141.
Typical prior art hot water heaters comprise a generally cylindrical storage tank, and heating means to heat the water stored in the tank. In direct fired water heaters the heating means may take the form of a gas burner located at the base of the cylindrical tank (as shown in U.S. Pat. Nos. 817,589 and 2,187,917) or electrical heating elements extending into the tank (shown in U.S. Pat. No. 2,303,126). The cold water usually enters through the top of the tank passing downwardly in a tube and exiting near the bottom of the tank. When heated, the water rises and is drawn off by a hot water exit tube.
Indirect fired water heaters are also known. They differ from the aforementioned directed fired type insofar as the heater water within the storage tank is not withdrawn and used, but acts as a heat exchange medium. Cold water in the storage tank is warmed by a heat exchanger with the heated water. No direct contact is made with the heating means or the heated stored water.
Most of the prior art water heaters, whether the direct or the indirect type, use some form of insulation around the exterior of the tank to prevent undue loss of heat by radiation. Solid flexible insulation is placed around the tank and retained in position by an outer wall, as shown in U.S. Pat. Nos. 2,303,126 and 2,187,917.
It is also known to make a water storage tank having concentrically arranged inner and outer tanks with a vacuum insulating space therebetween (U.S. Pat. No. 1,327,693). However, such tanks are normally used only for the storage and not the heating of water, since the insulating space on the bottom would prevent heat transfer between a burner and the inner tank.
Containers having inner and outer spaced apart walls with an insulating vacuum therebetween are shown in U.S. Pat. Nos. 1,511,852 and 1,673,653. These containers are used to store a liquid and to prevent transfer of heat to or from the liquid. See also U.S. Pat. Nos. 999,672, 1,691,912, 2,666,979 and 3,123,054.
See further U.S. Pat. Nos. 2,794,570, 3,064,344, 2,787,216, 3,247,999, 2,721,580, 2,302,835, 3,132,761, 3,057,509, 2,620,963 and 2,809,762.